Microelectronic imagers are used in digital cameras, wireless devices with picture capabilities, and many other applications. Cell phones and Personal Digital Assistants (PDAs), for example, incorporate microelectronic imagers for capturing and sending pictures. The use of microelectronic imagers in electronic devices has been steadily increasing as imagers become smaller and produce higher quality images with increased pixel counts.
Microelectronic imagers include image sensors that use Charged Coupled Device (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS) systems, or other systems. CCD image sensors have been widely used in digital cameras and other applications. CMOS image sensors are also becoming very popular because they have low production costs, high yields, and small sizes. CMOS image sensors provide these advantages because they are manufactured using technology and equipment developed for fabricating semiconductor devices. CMOS image sensors, as well as CCD image sensors, are accordingly “packaged” to protect their delicate components and provide external electrical contacts.
FIG. 1 is a schematic view of a conventional microelectronic imager 1 with a conventional package. The imager 1 includes a die 10, an interposer substrate 20 attached to the die 10, and a housing 30 attached to the interposer substrate 20. The housing 30 surrounds the periphery of the die 10 and has an opening 32. The imager 1 also includes a transparent cover 40 over the die 10.
The die 10 includes an image sensor 12 and a plurality of bond-pads 14 electrically coupled to the image sensor 12. The interposer substrate 20 is typically a dielectric fixture having a plurality of bond-pads 22, a plurality of ball-pads 24, and traces 26 electrically coupling bond-pads 22 to corresponding ball-pads 24. The ball-pads 24 are arranged in an array for surface mounting the imager 1 to a board or module of another device. The bond-pads 14 on the die 10 are electrically coupled to the bond-pads 22 on the interposer substrate 20 by wire-bonds 28 to provide electrical pathways between the bond-pads 14 and the ball-pads 24.
The imager 1 shown in FIG. 1 also has an optics unit including a support 50 attached to the housing 30 and a barrel 60 adjustably attached to the support 50. The support 50 can include internal threads 52, and the barrel 60 can include external threads 62 engaged with the threads 52. The optics unit also includes a lens 70 carried by the barrel 60.
One problem with conventional packaged microelectronic imagers is that they have relatively large footprints and occupy a significant amount of vertical space (i.e., high profiles). For example, the footprint of the imager 1 in FIG. 1 is the surface area of the bottom of the interposer substrate 20, which is significantly larger than the surface area of the die 10. Accordingly, the footprint of conventional packaged microelectronic imagers can be a limiting factor in the design and marketability of picture cell phones or PDAs because these devices are continually shrinking to be more portable. Therefore, there is a need to provide microelectronic imagers with smaller footprints and lower vertical profiles.
Another problem with conventional microelectronic imagers is the manufacturing costs for packaging the dies. The housing 30 shown in FIG. 1 is relatively expensive to form and mount because the transparent cover 40 must be properly aligned and mounted in the opening 32 and then the housing 30 must be positioned and mounted to the interposer substrate 20. This process can be subject to error and is generally time-consuming. Moreover, forming the wire-bonds 28 on the imager 1 shown in FIG. 1 is complex and expensive because it requires connecting an individual wire between each bond-pad 14 on the die 10 and a corresponding interior pad 22 on the interposer substrate 20. In addition, it may not be feasible to form wire-bonds for the high-density, fine-pitch arrays of some high-performance devices. Therefore, there is a significant need to enhance the efficiency and reliability of packaging microelectronic imagers.
Yet another problem of the conventional imager 1 shown in FIG. 1 is that moisture and/or other contaminants can impair the performance of the imager 1. Even though the die 10 is packaged within a cell formed by interposer substrate 20, housing 30 and cover 40, moisture or other contaminants can get into the cell. For example, the seals of the substrate/housing and the housing/cover interfaces can fail because of faulty materials or assembly. The seals at these interfaces can also fail because the different coefficients of thermal expansion between the substrate 20, housing 30 and cover 40 induce strain at the interfaces that can break the seals. Moisture may also be stored in the substrate 20 and expelled into the cell at elevated temperatures. This is more likely with substrates formed from organic materials. Therefore, there is also a need to improve the integrity of the package to enhance the protection of the image sensor.